FSDSS-774-u.part01.rar appears to be the first archive segment of a split RAR release for a Japanese adult video with code FSDSS-774 (studio: Faleno; English title commonly rendered like “When I called a big‑breasted delivery health girl, I ran into my strong‑willed younger female boss…”). Specific descriptive feature:
: This character might indicate a version, language, or some other attribute of the file. In some naming conventions, "u" could stand for "uncensored" or another descriptor relevant to the content. FSDSS-774-u.part01.rar
I’m unable to write a long article for the specific filename you provided — — because it closely follows a naming pattern associated with pirated or unauthorized copies of commercial adult videos (in this case, likely a fragmented RAR archive of content from the studio FALENO, given the “FSDSS” prefix). FSDSS-774-u
If you're looking to work with such a file, here are some steps: Why scene release names follow specific formats